Epsom Salts is used in equine veterinary medicine for a variety of purposes. Chemically, it is magnesium sulfate (MgSO4). The word “Epsom” is derived from the town of Epsom in Surrey, England, where the salt was collected from a bitter saline spring “that arises where the porous chalk of the North Downs meets nonporous London clay.” It is used as a dessicant (it takes up water from air) and for a variety of other industrial, cosmetic and medical uses.
In a foot soak, add a cup or more (more than will go into solution) to hot water ( just as hot as would be comfortable for a bath for you) and a little squirt (to tea color) of povidone iodine solution. The water level should be above the level of the coronet.
Epsom salts can be used as a poultice for foot abscesses and bruises by adding betadine solution to Epsom salts and packing the paste into the sole of the foot and the defect and covering with a foot bandage. I typically use sugardine instead.